The present invention relates to a nonvolatile memory device and to a technique that can be effectively applied to, for instance, flash memory cards, hard disk-compatible flash disks, and the like.
Rewriting of stored information in an electrically rewritable nonvolatile memory, typically a flash memory, involves electrical stresses in memory cells, whose performance characteristics would deteriorate with an increase in the frequency of rewriting. If rewrites locally concentrate, only some data blocks markedly deteriorate in characteristics. There is a technique to solve this problem by which data and addresses are automatically relocated into other areas when the frequency of rewriting has reached a certain level, and the useful life of the nonvolatile memory is extended in terms of the permissible frequency of rewriting. For instance, when the frequency of rewriting surpasses a prescribed level, the address allocation in data blocks is altered (see Patent Reference 1). There is also a technique by which the address allocation in data blocks is altered when the number of ECC errors surpasses a prescribed level (see Patent Reference 2).
[Patent Reference 1]
Japanese Unexamined Patent Publication No. Hei 04 (1992)-507320 (U.S. Pat. No. 5,172,338)
[Patent Reference 2]
Japanese Unexamined Patent Publication No. Hei 02 (1990)-118997 (U.S. Pat. No. 5,043,940)